1. Field of the Invention
Embodiments of the present invention generally relate to local tone mapping for high dynamic range images.
2. Description of the Related Art
The demand for higher dynamic range is a driving force for various imaging applications such as, for example, security cameras and automobile cameras. Imaging devices such as video cameras may be equipped with high dynamic range (HDR) sensors. Non-HDR cameras take photographs with a limited exposure range, resulting in the loss of detail in bright or dark areas. Some HDR imaging devices may compensate for this loss of detail by capturing two or more images at different exposure levels and combining the images to produce images a broader tonal range than non-HDR devices. Merging multiple exposures preserves both the saturated and the shadow regions and thus provides a higher dynamic range than a single exposure.
There are several known techniques for generating an HDR image (also referred to as a wide dynamic range (WDR) image) from two or more exposures. In one technique, the exposures may be spatially interleaved. In some techniques, the imaging system merges multiple exposures and provides a native HDR Bayer image with a pixel depth ranging from 12 to 20 bits. In some techniques, the imaging system captures multiple temporally spaced exposures and these exposures are merged to form an HDR image in the imaging device receiving the multiple exposures. Whether the imaging system generates the HDR image or the imaging device generates the HDR image, tone mapping may need to be performed on the HDR image to permit processing of the HDR image in an imaging pipeline with a lesser pixel bit depth, e.g., 10 to 12 bits.